Apparatus for making tire fabric impregnated with rubber

ABSTRACT

An apparatus for manufacture of a tire component said component being a sheet of reinforced unvulcanized rubber compound having two parallel main surfaces. The apparatus comprises an open mould shaped to accommodate the component arranged to contact one of said surfaces, a pressurizing member to contact the other said surface, and apparatus for maintaining the time/temperature conditions of the mould and the component below those required to cause vulcanization. The pressurizing member applies substantial compressive force to the component so that the rubber compound is pressed into intimate contact with the reinforcement. The apparatus provides real penetration of the rubber compound into the reinforcement and is particularly valuable for tire breakers which are steel cord reinforced.

This is a division of application Ser. No. 625,817 filed June 28, 1984,and now U.S. Pat. No. 4,689,101.

This invention relates to tire manufacture and in particular to themoulding of tires and reinforced tire components which are reinforced bysheets of reinforced fabric.

Tires are reinforced by textile or metal reinforcement cords which arein the form of sheets of fabric coated with unvulcanized rubber whichwhen cured provides the essential integrity between the cords of thefabric and other tire components such as, for example, the rubber tread.The coating of reinforcement cords with unvulcanized rubber is usuallycarried out by passing an assembled sheet of cords (i.e. the fabric)through the nip of a pair of calendar rolls together with rubbercompound which is pressed or positioned between the reinforcement cordsto form a handleable sheet. The pressures exerted on the rubber againstthe wires are low, of the order of 50 psi, and last for only a veryshort time through the nip and at the time of applications of pressurethe cords are held under tension through the rollers. The result is thatthe cords being tensioned are tightly wound and no real penetration ofthe rubber into the wires of each cord occurs. Considerable developmenteffort has gone on, particularly in recent years, to solve this problemwithout success and the lack of good rubber penetration is well known toallow the spread of moisture and rust along the wires in the cords ofsteel breakers. Such calendaring processes are used for filler strip,carcass fabric and breaker fabric. Subsequently the completed tire ismoulded in a tire press where high pressures, typically up to 400 psifor truck tires, are applied to the tire as it is heated to vulcanizethe rubber components. The high pressures and the heat of the pressproduce interply and intercomponent bonds and also move entrapped airand moisture into very small volumes such that generally satisfactorytires result. Nevertheless failures do occur in service with componentseparation, e.g. tread separation and breaker separation and in anyevent the pressures required in tire presses and moulds makes them veryexpensive items of capital equipment.

One object of the present invention is to provide a method ofmanufacture for tire components including sheets of reinforcement fabricwhich gives improved rubber penetration into the reinforcement fabricprior to assembling the component to the tire.

According to one aspect of the present invention a method of manufacturefor a sheet of reinforced unvulcanized rubber compound having twoparallel main surfaces comprises precoating the reinforcement materialfabric with unvulcanized rubber compound, placing the precoated fabriccord sheet in an open mould shaped to accommodate the precoated fabriccord sheet arranged to contact one of said surfaces, positioning apressurizing member to contact the other said surface, maintaining thetime/temperature conditions of the mould and the precoated fabric cordsheet below those required to cause vulcanization, operating thepressurizing member to apply substantial compressive force to theprecoated fabric cord sheet so that the rubber compound is pressed intointimate contact with the reinforcement and removing the unvulcanizedprecoated fabric cord sheet from the mould.

Two or more precoated fabric cord sheet may be precoated and assembledtogether into the open mould so that the two or more precoated fabriccord sheet are compressed together.

The reinforced ply are preferably breaker plies for a tire made indiscrete lengths having the length required for one full circumferenceof the tire.

Preferably the ply are each joined end-to-end to form annular ply andthe open mould is annular so that the ply are pressurized in therequired annular form for a tire.

In the above method the mould and precoated fabric cord sheet within themould may be heated to assist rubber flow into the reinforcement but thetemperature is in all cases kept below vulcanization temperatures,temperatures in the range 60°-80° C. are particularly effective.

According to another aspect of the invention an apparatus for the methodof manufacture of a tire precoated fabric cord sheet comprises anelongate rigid mould defining an open mould cavity shaped to accommodatethe reinforced precoated fabric cord sheet and contact one side thereof,a pressurizing member having means to position it to contact the othersurface of the precoated fabric cord sheet and close the mould cavity,and means to control the mould temperature so that vulcanization doesnot occur in the mould.

Preferably the rigid mould is a ring and the open mold cavity is on theinner surface of the ring and the pressurizing member provides anannular pressurization surface. The pressurizing member is preferably aradially narrow section inflatable tubular bag which has a width in theaxial direction greater than the width of the mould cavity.

It is most important that the precoated fabric card sheet isunvulcanized so that it may be shaped during subsequent tire buildingand to provide good adhesion to other components.

Further aspects of the present invention will be apparent from thefollowing description, by way of example only, of two embodiments inconjunction with the attached diagrammatic drawing in which:

FIG. 1 is a radial cross-section of part of an annular tire breakerpackage mould, and

FIG. 2 is a radial cross-section of part of an alternative annular tirebreaker package mould.

The mould shown in FIG. 1 comprises an annular steel ring 1 which hasmachined into its radially inner surface a set of three grooves 2, 3 and4. The grooves 2, 3 and 4 are dimensioned to fit the respective steelcord reinforced breaker plies 5, 6 and 7 for a truck tire. Groove 4 ismade deeper than the thickness of the breaker ply 7 to include also apair of stainless steel edge rings 8 and a central stainless steelcompression transmitting ring 9. The compression ring 9 and edge rings 8are cut so that they may expand radially by a small amount. The ring 1includes electrical heating elements which are arranged to heat themould to a temperature of about 80° C.

A pressurizing member assembly 10 is positioned inside the mould 1 andhas an outer radius a small distance G less in radius than the mould 1(note G is shown larger in the drawing for clarity than would be used inpractice). The pressurizing member assembly 10 comprises an annularsteel support ring 11 and a hollow rubber expander bag 12. An inflationvalve 13 is also provided which is connected to a source of highpressure fluid (not shown).

The mould is used to compress together breaker plies precoated in rubberto give good penetration of the individual steel wires in eachreinforcement cord and able to give good bonding between the breakerplies using the following steps. Firstly the pressurizing memberassembly 10 is moved axially out of the mould 1 to allow access. Thefirst breaker 5 is then prepared by assembling a sheet of reinforcementcords, coating both sides of the sheet with unvulcanized rubber toppingcompound and cutting the assembly at a bias angle to give the requiredcord angle in the breaker ply (usually of the order of 20°-30°) but maybe other angles including 0° to the longitudinal centre line). The firstbreaker ply 5 is then laid into the groove 2 in the mould 1. The othertwo breakers 6 and 7 are prepared and fitted into the mould in the sameway and finally the edge rings 8 and compression ring 9 are sprung intoplace as shown.

The pressurizing member assembly 10 is then moved axially into positionwithin the mould 1 and hydraulic pressure is applied to the expander bag12 to expand the stainless steel rings 8 and 9 and compress the breakers5, 6 and 7 together. The high pressure 1000 psi (66 bar) and the heatingof the mould which is typically to a temperature of 80° C. causes therubber topping compound to penetrate the reinforcement cords and adhereto each wire. Treatment also provides improved breaker ply to breakerply adhesion in a finished tire even though the tire has been cured atnormal curing pressures. Thus it is no longer essential to use highpressures during final tire assembly vulcanization in order to achievethese benefits.

After treatment the breaker package is removed from the mould by axiallymoving the pressurizing member assembly 10 from the mould and radiallycollapsing the breaker which, being unvulcanized, is a fairly flexiblering.

While the mould has been described as an annular one-piece mould itshould be appreciated that it may be a two-piece or a multi-segmentmould which is assembled around the breaker package. This assistsremoval of the compressed breaker from the mould. Furthermore the mouldand associated pressurizing member may be straight components ratherthan annular and used to form discrete lengths of impregnated material.

The mould shown in FIG. 2 is again an annular tire breaker mould but isintended for car tire breakers. More specifically it is for a 155SR12radial car tire with a steel breaker which is a two-ply breaker. Itcomprises an annular steel ring 14 which has machined into its radiallyinner surface a single groove 15 which is a 12 cms wide and 0.2 cms deepand the annulus has a diameter of 56 cms so that a breaker package of 56cms diameter is made.

A pressurizing member 16 is mounted on a central steel support ring 17and comprises a narrow section, expandable bladder 18 which has provideda fluid inlet port 19. The bladder 18 comprises a rubber bag reinforcedby two plies of polyester tire cord fabric and has a width wider thanthe groove 15. The bag wall thickness is between 0.1 and 0.2 cms.

The upper surface 20 of the bag is covered with a non-stick material andthe gap between the steel ring 14 and the support ring 17 is 1 cm sothat the bladder 18 is in a narrow annular space as shown. Thus the foldradius of the bladder edges is about 0.5 cms and pressures up to 90 barmay therefore be safely used with a tire cord reinforced bladder 18.

The apparatus is operated in the same way as the first embodiment exceptthat the intermediate force transmission components are omitted.

By high pressure is meant pressures greater than 500 psi (33 bar) andpressures in the range of 60-120 bar have been found particularlyeffective in producing penetration much better than hitherto.

It is most important to understand that the cords of the fabric areuntensioned throughout the process which is quite different from knownprocesses including calendaring and tire curing in a press and thisgives great advantage as the rubber compound is therefore not preventedfrom entering the cord by the usual filament to filament contacts.

In a specific example, two 11 R 22, 5 SP 111 tires were moulded usinghigh pressure 375 psi hot water cure in a Bagomatic Press.

One contained a breaker band comprising 4 plies which were precompressedat 1000 psi at 80° C. for 30 minutes. The other tire was a normalproduct built tire where the breakers were assembled one at a time ontoa shaped carcass.

Both sets of breakers were originally coated with rubber compound bycold calendering i.e. the normal production process.

After manufacture both tires were examined and ten wires were removedfrom the third breaker on each tire leaving the rubber coating intact. Arubber sleeve was moulded around each individual wire and a source ofhigh pressure air (100 psi) was connected to one end of each wire inturn and the flow rate through the wire was measured by a flowmeter.

The results of these tests averaged out for the ten wires from each tirewere as follows:

Precompressed breaker tire (1000 psi) as per invention: 109 cc/min

Normal production tire: 633 cc/min

This clearly shows the great reduction in air flow which proves the muchimproved rubber penetration into the cord when treated according to thepresent invention.

Temperatures in the range of 60°-80° C. are also advantageous inproducing the good penetration without vulcanization. The choice oftemperature depends on the time the component is in the mould and thecord construction and may for some tire compounds be well in excess of80° C.

Fitting steel reinforced compoents into the mould may be assisted byusing magnets in the mould and it is also sometimes useful to use anon-stick coating on the mould to prevent sticking as the compoundremains unvulcanized after impregnation.

Furthermore as in the second embodiment the stainless steel compressionmember is not always essential and when it is not used alternativeanti-stick members such as polythene sheeting may be used to avoidsticking to the pressurizing bag.

The source of high pressure fluid may be pneumatic or hydraulic althoughthe latter is preferred for safety reasons.

Finally while the process is particularly valuable for tire breakermaterial it is also effective for carcass and filler reinforcementmaterial. The reinforcement material impregnated may be steel ortextile.

I claim:
 1. An apparatus for use in the manufacture of a cord reinforcedelastomeric tire breaker comprising at least two plies, and which is forconsolidation of an annular breaker,said apparatus comprising a rigidmold in the form of a ring having an open annular mold cavity on itsradially inner side to accommodate an annular precoated rubberizedbreaker and which is in the form of a plurality of shallow steppedgrooves each groove being dimensioned to receive a respective breakerply, a wall of the cavity contacting one side of said breaker fabricsheet; a pressurizing member supported on a rigid carrier and havingmeans to position it to contact the other surface of the sheet and closethe mold cavity, said pressurizing member comprising a bag inflatable byfluid pressure, with a pressure transmitting ring located between thebag and the breaker, and control means in the mold to control the moldtemperature so that vulcanization does not occur in the mold.
 2. Anapparatus according to claim 1, wherein the pressurizing membercomprises a radially narrow section inflatable tubular bag which has awidth measured in the axial direction of the mold ring, substantiallygreater than the width of the mold cavity.
 3. An apparatus according toclaim 2, wherein the bag is reinforced by cord fabric.
 4. An apparatusas claimed in claim 1, wherein the control means in the mold includeheating elements arranged to heat the mold to a temperature of around80° C.
 5. An apparatus as claimed in claim 1, wherein the radiallyinnermost groove is deepened to accept the pressure transmitting ringand the respective breaker ply.
 6. An apparatus as claimed in claim 1,wherein the mold can withstand a pressure of about 1000 psi which isgenerated by hydraulic pressure within said bag.